Generally speaking, most people put their bodies under varying degrees of impact during exercise, and it has been established that the forces exerted on the heel and the ball or front sole of the feet during running are three to four times greater than those exerted during normal walking. Thus, during running or jogging, the reaction forces exerted on the body from the ground may be three to four times higher than individual body weight. Not only is this the cause of many sports injuries, but also it makes the participants tired or exhausted. Sports shoes for running or jogging or playing games and casual shoes for walking are commercially available in a variety of designs, but, generally speaking, the soles of such shoes and consequently the shoes in their entirety do not match the individual requirements of the wearer as regards providing the desired degree of resilience and elasticity.
It is known to provide means in a sports shoe for enabling the characteristics of the shoe to be adapted to the requirements of the user. For example, U.S. Pat. No. 4, 430, 810 discloses an arrangement wherein a number of bores extend through the relatively soft material of the heel portion of a running shoe from one side thereof to the other, the bores being spaced apart from each other in the longitudinal heel-to-toe direction of the shoe, and rod-shaped stiffening members of selectable greater hardness than the soft heel material can be inserted into the bores so as selectively to increase the overall hardness of the sole and adapt the shockabsorbing capabilities of the shoe to the individual requirements of the runner and to the nature of the surface upon which he intends to run. The proposal to stiffen the heel of a shoe by insertion of appropriate stiffening elements into bores in the heel is known also from French Patent No. 958,766, and in U.S. Pat. No. 3,785,646 discloses a shoe having a rubber sole with transverse bores into which rod-like metal weights may be inserted. Another arrangement, known from applicants British Patent No. 2,156,654, not only enables heel hardness characteristics to be selectively varied to suit the requirements of the wearer, but also allows different relative hardnesses to be achieved on different sides of the heel for controlling rear-foot movement and minimizing the risk of damage through excessive pronation or supination. Another known arrangement of only marginal interest to the present invention is disclosed in European Patent Application Ser. No. 0161653.
It is further known to incorporate air pockets into the heel portion and/or the sole portion of a shoe so as to provide shock absorption and/or resiliency properties. Described in British Patents Nos. 2,150,0010 and 2,183,446 are shoes which incorporate an inflatable bladder within a cavity in the heel portion of the shoe, the degree of inflation of the bladder in each case being selectively variable. The shoe of British Patent No. 2,150,010 also incorporates a plurality of sealed air pockets generally in the metatarsal region of the ball of the foot. Disclosed in European Patent Application Serial No. 0160880 is a molded shoe sole wherein air can transfer between cavities defined by bulges molded into the sole and heel portions for providing shock absorption and movement facilitation characteristics, though without any possibility of adjusting the air pressure within the cavities. An arrangement similar to that disclosed in European Patent Application Serial No. 0160880 is described in British Patent Application No. 2,073,006, and in the latter case means are provided to enable the desired fluid pressure in the interconnected cavities to be determined. A shoe provided with a selectively inflatable insole is described in British Patent No. 358,205. The shoe described in International Patent Application No. WO 82/00571 has a gas pressure chamber in its sole and includes a pump arrangement which keeps the gas pressure constant. Other shoes incorporating pneumatic structures in their heel and/or sole portions are described in British Patent Specifications Nos. 390,368, 490,647, 2,023,405 and 2,034,169 and in U.S. Pats. Nos. 4,183,156, 4,219,945 and 4,271,606.
None of the aforementioned documents discloses a sports shoe, or a sole for such a shoe, which affords to the user the degree of selectable resilience that is afforded by a pneumatic sole structure having means for pressure adjustment, coupled with selectability as regards the distributed hardness characteristics within the sole and/or heel region.